In various cases, cooled turbine blades or vanes (guide vanes and/or rotor blades) with cooling-air holes have incorrect, in particular excessive, flow rates of the stream of cooling air. This has a negative effect on the efficiency of the gas turbine. The air compressed in the compressor is used as little as possible for cooling, but instead should be fed to the combustion process. Cooling-air openings are understood to mean the following: a cast or bored outlet edge, stem bores (longitudinal bores), EDM or laser shapes (diffusers), cylindrical EDM or laser bores.
The fault pattern or the flow rate to be optimized is often determined relatively late in the process chain.
The declaration of the components as rejects is therefore very costly.
Examples for excessive flow rates are:
faults in the casting; in the boring process; faults in the boring process during upgrades; additional ceramic coating or an increase in the layer thickness or a reduction in conductivity during refurbishment; the base material can also be attacked by the acid during stripping or reworking, such that the size of the cooling-air openings is increased.